The present invention relates to a multiple-stage blending screw with a unique configuration, which is suitable for transporting plastic raw materials in an extruder for plastic molding as well as for thoroughly blending the plastic raw materials, so that the quality of the extruded plastic material is uniform and suitable for the manufacture of high-quality products.
A conventional plastic extruder consists typically of a main body and a screw, which are configured in such a manner that the threads of the screw come into contact with the inner surface of the main body. When a plastic raw material is fed into an inlet to the main body while the screw is turning, the plastic raw material gathered in the valley of the screw, is being pushed forward and extruded by the rotation of the screw. However, this configuration is subject to the following drawbacks:
(1) Since the plastic raw material accumulates in the valleys of the screw and is then pushed forward by the screw's rotation without any mixing action, the plastic raw material is not properly blended. As a result, the plastic raw material so extruded lacks uniformity, which affects the quality of the resulting injection plastic products.
(2) Since the front of the screw comes into contact with the main body at an oblique angle, the supporting point varies, thereby bringing about a certain degree of deviation from the center of gravity. As the screw rotates, which sends the plastic raw material forward, the back pressure causes the pressure at the front end to become uneven. As a result, the friction at the front end increases substantially; this damages the inner wall of the main body, causes the raw material to be extruded unevenly, and reduces the amount of raw material being extruded.